Electric motors usually generate heat during operation. In some applications, the motors are required to be cooled to avoid damage caused by overheating so as to ensure normal operation.
U.S. Pat. No. 7,675,209 discloses a cooling device of a dry-liquid cooled electric motor. The cooling device surrounds the iron stack and winding of the stator of the motor. Cooling liquid is circulated through channels within the cooling device and heat is transferred from the stator through direct contact of the stator with the cooling device. The cooling device has an inner sleeve and an outer sleeve. The outer sleeve surrounds the inner sleeve forming a circular space between the outer sleeve and the inner sleeve. A continuous winding path is arranged within the circular space and extends axially back and forth along the circumference of the inner sleeve. The inner sleeve includes an end section with a bearing housing and two openings functioning as an inlet and an outlet. The inlet and the outlet are positioned diagonally across from each other at one axial end of the cooling device. As the temperature of the cooling liquid gradually increases after the cooling liquid enters into the winding path, the temperature of the cooling liquid near the inlet is lower than the temperature of the cooling liquid near the outlet, and thus the stator can not be evenly cooled in the circumferential direction. Besides, the end section with the bearing housing increases the axial length of the motor.
Hence there is a desire for a cooling device for an electric motor which provides even cooling of the stator core.